Vibration Energy Harvesting (VEH) is a relatively new concept relating to the conversion of mechanical energy (resulting from a vibration) to electrical energy for subsequent use or store. Typically, the mechanical to electric conversion is performed using either an electromagnetic transducer or a piezoelectric transducer, though many other transducer types may be utilised.
Vibration rich environments suitable for energy harvesting can be found in almost every facet of everyday life. For example, through the simple action of walking, a vibration is experienced which could potentially be harvested and used to power a device, such as, for example, a mobile phone.
Generally, present arrangements for VEH propose the use of a harvesting circuit configured to extract the energy in electrical form from the transducer and drive a load (such as a mobile phone). The harvesting circuit includes components that provide impedance or components that are controlled to synthesise an impedance or admittance (e.g. a controlled switch circuit). The impedance is generally chosen in an attempt to “match” the mechanical and transducer system from which the energy is harvested, in an attempt to obtain optimum energy transfer.
Vibrational energy tends to be “bursty”; however, occurring as discrete (and sometimes unpredictable) bursts (e.g. when a step is taken when a person is walking). Energy is not harvested efficiently, even where a harvesting circuit is designed which effectively impedance matches the mechanical and transducer system.